Radio communication systems that utilize simulcast transmissions are in wide use today. A typical example is a radio paging system. Simulcast transmissions, in which a single information signal is simultaneously transmitted from a plurality of geographically disperse transmitters to provide radio coverage over a wide geographic area, are employed in most wide area radio paging systems.
Whenever the number of users of a simulcast radio communication system increases within a given geographic coverage area, communication traffic can eventually reach the capacity limits of the system, and steps must be taken to increase the traffic capacity of the system before additional geographic coverage areas and users can be accommodated. One step that is often taken is to add another radio channel to the system. That step, is at best expensive, and may be impossible in some locations where all available channels are occupied.
Conventional radio paging systems, including acknowledge-back communication systems, have utilized simulcast fixed-to-portable radio transmissions that operate ubiquitously, i.e., simulcasting substantially every fixed-to-portable communication from substantially every fixed transmitter in the system. If, however, there could be found a way of locating portable communication units as they move about the system, then the number of base transmitters and receivers utilized for communications with any one individual portable communication unit could be isolated only to those fixed transmitters and receivers near each portable communication unit. This isolation would allow simultaneous reuse of base transmitters, receivers, and communication spectrum for additional communication with other portable communication units in other parts of the geographic coverage area of the system on the same radio channel.
Thus, what is needed is a method and apparatus for increasing the capacity limits of a simulcast radio communication system in a manner that does not require an additional radio channel.